Continuously variable transmission for a motor vehicle

ABSTRACT

A continuously variable transmission ( 1 ) for a vehicle comprising one variator ( 4 ) with a non-positive, special friction-type, power transmission such as a friction gear or a conical disk continuously variable transmission is described wherein the transmission input power can be divided into at least two performance ranges and can be transmitted in a first performance range either by means of a first power split ( 2 ) via the variator ( 4 ) or by means of a second power split ( 3 ) by-passing the variator ( 4 ), or by means of both power splits ( 2, 3 ). According to the invention the transmission performance is power split in the first and second performance ranges.

FIELD OF THE INVENTION

The invention concerns a continuously variable transmission for avehicle comprising one variator with a non-positive, specialfriction-type power transmission such as a friction gear withinteracting toroidal treads disposed in pairs between which rollerbodies rotate, or a conical disk continuously variable transmission anda first planetary gear. The transmission input power can be divided inat least two performance ranges wherein, in one performance range, thepower can be transmitted either by a first power split from atransmission input via the variator, the same as the first planetarygear, to a transmission output or by a second power split from thetransmission input via a mechanical split by-passing the variator to thefirst planetary gear and the transmission output, or power split bymeans of both power splits.

BACKGROUND OF THE INVENTION

Such a friction gear is already known from the Applicant's WO 98/34051.The problem to be solved by the invention was to improve, with regard tototal efficiency achievable, a transmission operated in two performanceranges and, furthermore, to be able to adapt the transmission withbasically the same design to different installation conditions. In thesecond performance range, the transmission input power is transmitted tothe output shaft with a power split in the transmission.

In such a continuously variable vehicle transmission, a reduction of thetorque in the variator is proposed only in one performance range as itis known from the prior art. From the field of hydrostatictransmissions, power split transmissions, which disadvantageously have astrong noise development with poor efficiency and also high costs ofproduction, are further known.

The problem to be solved by this invention is to provide a continuouslyvariable vehicle transmission which overcomes the above mentioneddisadvantages and especially makes a reduction of the variator load overthe whole performance range and an improved efficiency possible.

SUMMARY OF THE INVENTION

The problem is solved, according to the invention, in a general vehicletransmission by the fact that the transmission power is split both inthe first and in the second performance ranges and can be transmittedfrom the transmission input to the transmission output, via the firstand the second power splits. By virtue of such a split powertransmission in the first and in the second performance ranges, acontinuously variable vehicle transmission results which advantageouslymakes a small variator load in both performance ranges possible incomparison to a transmission without a power split or to a transmissionwhich has power split in only one performance range. A better efficiencyof the continuously variable vehicle transmission is further obtained bythe power split. Compared to the transmission without a power split, agreater transmission spreading is advantageously made possible.

In one special development of the invention, it is proposed to provide asecond planetary gear, for power split in both performance ranges, andthen to add up again in the first or the second planetary gear the twopower portion which have been passed via the first and second powersplits. It is thus advantageously obtained, a simple and economicalmeans of implementing the power split in both performance ranges of theabove mentioned vehicle transmission.

At least one of the two planetary gears is advantageously situated inthe power flow between the transmission input and the transmissionoutput parallel to the variator or also located downstream of thevariator.

In one development, both planetary gears are disposed in the power flowparallel to each other between the transmission input and thetransmission output.

The first and the second planetary gears are advantageously disposed sothat in the first performance range the variator is connected with thesun gear of the first planetary gear, the transmission input with theplanet carrier and the transmission output with the ring gear of thefirst planetary gear.

In addition, the first and the second planetary gears are disposed sothat in the second performance range, the variator is connected with thering gear of the second planetary gear, the transmission input with thesun and the transmission output with the stem of the second planetarygear.

In a preferred design of the invention, at least two clutches areprovided for connecting the two planetary gears which are situated indifferent places in the transmission according to the utilization of thetransmission or to possibilities of installation.

Both clutches can be shifted so that one planetary gear can be loadedwith power and the other planetary gear rotate along idlely withoutpower transmission.

In one development, both clutches are situated in the mechanical powersplit parallel to the variator.

To shift a reverse gear, one brake parallel to both clutches isadvantageously provided according to the preceding design.

In one other development, it is proposed that both clutches be providedin the power split of the variator and be located downstream thereof.Thereby both clutches are advantageously loaded with low torque.

In another development, both clutches are situated between the twoplanetary gears and the transmission output.

In a special development of the invention, in the first performancerange, the vehicle is driven out of a neutral geared position of thetransmission both in forward and in reverse. For driving in gearedneutral, no other driving element with a slip regulation, such as aconverter or a friction clutch, is basically required. Besides, anadditional reverse gear is not necessary, since it results from theratio of the continuously variable transmission.

BRIEF DESCRIPTION OF THE DRAWING(S)

Other objects, features, advantages and possible uses of the inventionresult from the description that follows of the embodiments which areshown in the drawings.

FIG. 1 is a basic representation of the power split in a continuouslyvariable transmission.

FIGS. 2 to 5 are design variants of a basic representation of theinventive continuously variable transmission with a variator and twoplanetary gears; and

FIG. 6 is a diagrammatic representation of a continuously variabletransmission with a power split for a front-transverse arrangement in amotor vehicle in diagrammatic representation.

DETAILED DESCRIPTION OF THE INVENTION

In a continuously variable transmission 1, the power split (FIG. 1),such as known from the prior art, is as follows:

A power delivered by a prime mover (not shown) is made available astransmission input power P_ein on the transmission input 8. In thetransmission 1, situated in a first power split 2, are a variator 4 witha reduction step 5 located downstream thereof and a first planetary gear6. Parallel to the first power split 2, a second power split 3 isprovided which has a reduction step 7. One part of the total powerexisting on the transmission input 8 is passed through the variator 4,the other part bypasses the variator 4 via the mechanical power split 3.Both portions are then added up again in the first planetary gear 6 andmade available as the transmission output power P_aus. The power isdivided in a defined manner, i.e. the power portions in the variator 4and in the mechanical split 3 result in accordance with the totalreduction ratio.

In FIGS. 2 to 5 that follow, different designs of a continuouslyvariable vehicle transmission with one variator 4 and two planetarygears 6 and 10, according to the invention, are shown and the parts thatrecur in the individual figures are designated with the same numeralsfor the sake of simplicity.

All FIGS. 2 to 5 have here the same basic arrangement of the essentialcomponents, these are: the variator 4, with the reduction step 5 locateddownstream, and the reduction step 7, disposed parallel thereto and thedownstream located planetary gears 6 and 10.

In the design of FIG. 2, first and the second clutches 11, 12 are placedin the first power split 2 between the reduction step 5 and the twoplanetary gears 6 and 10. Hence as shown, for example, the second clutch12 is engaged, the power split takes place via the two power splits 2and 3, the two power portions being added up again in the secondplanetary gear 10 while the first planetary gear 6 rotates along idlely.In such an arrangement of the clutches 11 and 12, these areadvantageously loaded with only a low torque since the passed powerportion passed, via the variator 4, is significantly reduced compared tothe power portion which would have been passed via the variator withouta power split.

In an alternative form of arrangement of the clutches (FIG. 3), theseare placed in the second power split 3 between the reduction step 7 andthe two planetary gears 6 and 10. In the design shown here, with secondclutch 12 engaged, the two power portions are added up in the firstplanetary gear 6 while the second planetary gear 10 over the disengagedfirst clutch 11 is not engaged and thus rotates along idlely.

In another possible form of arrangement (FIG. 4), the two clutches 11and 12 are disposed between the two planetary gears 6 and 10 and thetransmission output 9. In the arrangement reproduced here, with engagedsecond clutch 12 engaged, the power portions are added up in the firstplanetary gear 6 while the second planetary gear 10 rotates along idlelythrough the disengaged first clutch 11. By virtue of this arrangement ofthe two clutches 11 and 12 on the transmission output, the engagedclutch is loaded with the full transmission output torque.

The representation, according to FIG. 5, corresponds essentially to thearrangement of FIG. 3, but in the latter for the reverse gear range ofthe transmission, a brake 13 is provided to both clutches 11 and 12.Movement in the forward direction occurs, for example, by an engagedfirst clutch 11 or also with the geared neutral. To move in a reversegear direction, the brake 13 is engaged and the two clutches 11 and 12disengaged so that a torque, with a reverse direction of rotation, ismade available at the transmission output 9.

For a front-transverse arrangement (FIG. 6) of the inventivetransmission in a vehicle, the variator 4, the planetary gears 6 and 10and a differential 14 are consecutively arranged so that their mainaxles are respectively parallel to each other and extend across thevehicle longitudinal axis 15. Behind the transmission input 8, a powersplit occurs via the first power split 2 to the variator 4 and via thesecond power split 3 and a reduction step 7 to the planetary gears 6 and10. On the variator 4, in turn, a mechanical reduction step 5 is locateddownstream and is connected, via the clutches 11 and 12, with theplanetary gears 6 and 10. The transmission output power P_aus, from thetransmission output 9, is divided between the two input shafts 16 and 17via the differential 14.

What is claimed is:
 1. A continuously variable transmission (1) for avehicle having one variator (4) with a friction power transmission wherea transmission input power (P_ein) is dividable in to at least a firstand second performance ranges and where the power flow is diverted intoat least two power portions by at least a first and second split powerin the performance ranges, the continuously variable transmissioncomprising: at least a first planetary gear (6) and a second planetarygear (10); at least a first clutch (11) and a second clutch (12) forshifting the first and the second planetary gears (6, 10); atransmission input; a transmission output; a mechanical power split; abrake; in at least one performance range the transmission input powercan be transmitted by the first power split (2) from the transmissioninput (8), via the variator (4) and the first planetary gear (6), to thetransmission output (9), and by the second power split (3) from thetransmission input (8), via the mechanical power split by-passing thevariator (4), to the first planetary gear (6) and the transmissionoutput (9), wherein the brake (13) is provided parallel to the first andsecond clutch (11, 12) for shifting a reverse gear of the continuouslyvariable transmission (1).
 2. The continuously variable transmissionaccording to claim 1, wherein the second planetary gear (10) is providedfor both the first and second performance ranges for power splitting andeach of the first and second power splits (2, 3) are then recombined inone of the first and the second planetary gears (6, 10).
 3. Thecontinuously variable transmission according to claim 1, wherein atleast one planetary gear (6 or 10) in the power flow is arranged betweenthe transmission input (8) and the transmission output (9) and is one ofarranged parallel to the variator (4) and located downstream of thevariator (4).
 4. The continuously variable transmission according toclaim 1, wherein the first and second planetary gears (6, 10) arearranged parallel to one another in the power flow.
 5. The continuouslyvariable transmission according to claim 1, wherein the first and secondplanetary gears (6, 10) are arranged so that, in the first performancerange, the variator (4) is coupled with a sun gear, the transmissioninput (8) is coupled with a planet carrier and the transmission output(9) is coupled with a ring gear of the first planetary gear (6).
 6. Thecontinuously variable transmission according to claim 1, wherein thefirst and second planetary gears (6, 10) are arranged so that, in thesecond performance range, the variator (4) is connected with a ring gearof the second planetary gear (10), the transmission input (8) is coupledwith the sun gear and the transmission output (9) is coupled with a stemof the second planetary gear (10).
 7. The continuously variable vehicletransmission according to claim 1, wherein both clutches (11, 12) areshiftable so that each time one of the first and the second planetarygears (6 or 10) is loaded with power and the other of the first and thesecond planetary gears (10 or 6) rotates without power transfer.
 8. Thecontinuously variable vehicle transmission according to claim 7, whereinboth clutches (11, 12) are arranged parallel to said variator in themechanical power split (3).
 9. The continuously variable transmissionaccording to claim 1, wherein the first and second clutches (11, 12) arelocated downstream of the variator (4) in the first power split (2). 10.The continuously variable transmission according to claim 1, wherein inthe first power performance range, in a geared neutral position of thetransmission (1), the vehicle can be moved in both a forward directionand a reverse direction.